1. Field of the Invention
This invention relates to improvements in instruments for accomplishing near infrared quantitative analysis and particularly for improvements for correcting for wide temperature variations of both the ambient environment and the sample measured by such instruments.
2. Prior Art
Near infrared quantitative analysis instruments are known and commercially available. Such instruments known in the prior art make use of the phenomenon that certain organic substances absorb energy in the near infrared region of the spectrum. By measuring the amount of energy absorbed by the substances at specific wavelengths, precise quantitative measurements of the constituents of a product can be determined. For example, protein and moisture analysis in cereal grain can be determined by such instruments. For a general introduction to near infrared quantitative analysis, see the paper presented by Robert D. Rosenthal to the 1977 annual meeting of American Association of Cereal Chemists entitled "An Introduction to Near Infrared Quantitative Analysis".
Attention is also directed to the patent granted to Robert D. Rosenthal and Scott Rosenthal entitled "Apparatus for Near Infrared Quantitative Analysis" assigned to the assignee of this invention, U.S. Pat. No. 4,286,327 granted Aug. 25, 1981 and specifically to the prior art cited therein.
Some prior art near infrared quantative analysis instruments which measure the protein, moisture, etc., of cereal grain require the grain sample to be ground into small particles. It is highly desirable to be able to measure and analyze a sample of products without the need for grinding the sample. Grinding is time consuming, noisy and requires expensive equipment.
However, one serious problem results from attempting measurement by near infrared quantitative analysis of unground sample, especially if the sample is subject to widely varying temperature. This is due to temperature effects on the absorption wavelengths being measured. In the prior art near infrared instruments (e.g., of the reflected type) where a grinder was necessary to pulverize the sample prior to measurement, the grinding incidentally heated the sample to a constant temperature that was independent of the ambient temperature. Thus, when the ground sample was inserted into the prior art near infrared instruments, the sample was essentially at a constant temperature.
Near infrared quantitative analysis instruments are used quite often to measure the protein or moisture of grain in an out-of-doors location e.g., a grain elevator scale house and the temperature may vary from 40.degree. F. in the winter to as high as 120.degree. F. in the summer. This very broad temperature range will cause great inaccuracies in measurement of constituents of the products such as unground grain. This is because the moisture absorption wavelengths on which the instruments rely shift significantly with temperature and thus measurement of all the constituents (for example, protein, oil and moisture) is greatly influenced by this shift in moisture absorption peak. This adverse effect of temperature variation is true of measurements in the 1000 nm range (where measurements of this invention's commercial embodiment are made) as well as other absorption bands including the 1800-2500 nm band, where the prior art U.S. Pat. No. 3,776,642 is applicable.
It is known to provide near infrared instruments for protein analysis with internal heaters to heat its ambient to a temperature above the maximum that is expected to be encountered, e.g., such instruments normally operate at approximately 110.degree. F. to 120.degree. F. However, such internal heaters are expensive and wasteful of expensive power. The heat also adversly affects the reliability and life of the instruments' electronic components.
Of course measurement of the temperature of sample is a common place occurrence in laboratory instruments. Typical temperature measurement devices include thermocouples, thermopiles and other temperature measuring means that usually use the change in electrical property of a sample to measure the sample temperature. In the past, however, near infrared quantitative analysis instruments only used optical measurements. They have never previously combined more than one type of basic measurement, that is, to applicant's knowledge, the prior art never combined optical measurement with temperature measurement and linear regression correction in near infrared quantitative analysis instruments.